As described in commonly owned U.S. Pat. Nos. 4,900,074 and 5,476,294, a motor-vehicle door latch normally has a housing, a pivotal lock fork on the housing engageable with a door bolt and pivotal between a locked position engaged around the bolt and retaining it on the housing and an unlocked position permitting the door bolt to move into and out of the housing, a release pawl engageable with the fork and displaceable between a holding position retaining the fork in the locked position and a freeing position out of engagement with the fork and permitting the fork to move into the unlocked position, and a lever mechanism connected to the release pawl and movable between an actuated position displacing the pawl into the freeing position and an unactuated position with the pawl in the holding position Inside and outside handles operable from inside and outside the vehicle are connected to the lever mechanism to operate it and unlatch the door. Inside and outside lock elements are also connected to this mechanism to prevent at least the outside handle from operating the lever mechanism.
To prevent a door, normally a rear-seat door, from being accidentally opened, normally by a child, it has become standard to provide a so-called child-safety or -cutout system. This is typically embodied as an element that is exposed at the edge of the door when the door is open and that can be moved manually between an on and off position. In the on position the inside door handle is no longer operational.
Such a mechanism works in either of two ways: It can simply block actuation of the inside handle by putting some element in the movement path. Thus the inside handle cannot be moved at all. Alternately it can decouple the inside handle from the latch mechanism so that, even though the inside handle can be actuated, such actuation will have no effect.
The problem with this arrangement is that the vehicle operator frequently forgets to enable or disable the child-safety feature, leaving it off when children are being transported or leaving it on so adult passengers have to be let out of the back seat. The fact that the latches must be individually and manually set is the main reason this feature is not used more, and attempts to operate it via a power-lock system or the like have not proven practical or inexpensive enough to warrant broad use.